Pie Crust Superdome

I made two apple pies recently.

Both the pie filling and crust(s) recipe(s) come from Rose Levy Beranbaum's Pie & Pastry Bible. One crust was all butter. The other was flaky cream cheese, which she annotates as, "It took several years and over 50 tries to get it right and is the soul of this book". It is indeed a great crust, but I'm having problem with it (and the other crust as well).

The problem is stated thusly, "I fill the pies very full of apple pie filling such that there's a dome of fruit 3 inches high. I drap the pie crusts over the filling, seal the edges, brush with egg wash, cut a few slits in the top crust to let air escape, then bake at 425 F for 50-55 minutes. When the pie is baked, the filling is cooked down to about 2 inches, but the dome is still 3 inches, leaving a giant superdome full of air at the top of the pie. It's like the filling collapses, but the crust does not."

The crusts are high-fat (one all-butter, one butter-cream cheese). Very little liquid is used to bring the doughs together. The crusts have slits cut into them to let air escape, so I don't think it's a case of "inflation support", such that air inside is inflating the pie from within, holding the crust aloft.

The only thought that comes to mind is that 425 is too hot, so the crust is setting too quickly and setting hard, so it doesn't collapse (something I find strange considering how much enrichment these crusts have)?

It certainly makes a beautiful pie, but it looks ridiculous once cut with so much empty space between the filling and the crust.